Gel electrophoresis is a widely used method for separating biomolecules, such as proteins, peptides, nucleic acids etc. Gel electrophoresis involves the migration of electrically charged molecules in an electric field. A solution containing biomolecules is placed in contact with a supporting gel, an electric field is applied and the molecules are allowed to migrate on or through the electrophoretic gel. Electrophoretic separation of molecules is based on the difference in charge density of the molecules as well as the sieving effect of the porous gel media.
The normal procedure when electrophoresis is done in horizontal or vertical slab gels is to apply a number of samples and run them in parallel sample lanes so that the sample components in each lane separates into a number of bands. There are a number of reasons why the sample lanes should be kept as narrow as possible. One point is that decreased widths of the sample lanes allow a larger number of samples to be run on a gel slab of given size. Another point is that the sensitivity with which the biomolecules can be detected and measured is inversely proportional to the width of the sample lanes. Narrow lanes are also advantageous in situations, where the whole sample lane or parts of the lane after finished electrophoresis need to be transferred and use in connection with a second technique such as Western blotting, 2-D electrophoresis or tryptic digestion followed by MS.
With currently used techniques the width of the sample lanes are mainly determined by the width of the sample application zone. Easy and convenient manual sample application with a micro-pipette require a minimum width of the sample application zones of the order of 2-3 mm, but for best possible sensitivity the width of the sample lanes should be in the order of 0.2-0.5 mm. The combination of narrow sample lanes with the use of thin gels, required for best possible resolution, drastically limit the sample volumes possible to use. To use narrow high sample application cups on a thin horizontal gel is not a solution, unless the samples contain low salt and buffer concentrations. Due to the distortions of the electric field around a sample cup, used in this manner, the biomolecules will spread laterally as they leave the cup and enter the gel. The result is a sample lane much wider than the used application zone.
M W Swank et al (J Neurosci Meth 158 (2006) 224-233) describe slab gels where paper strips saturated with high ionic strength buffer are pressed onto the gel between the sample application zones, to provide an electric field gradient that gives some lateral focusing of the sample lanes. This setup is complex, requires careful manual handling, so there is a need for a more convenient solution.